The invention relates to perforating guns having selectable multiple configurations including phasing patterns and shot densities.
After a well has been drilled and casing has been cemented in the well, one or more sections of the casing may be perforated for either production or injection of fluids. Perforation operations are performed using perforating gun strings, which are lowered into the well to a desired depth and fired to create openings in the casing and to extend perforations into the surrounding formation.
Depending on the desired hole pattern to be created by a perforating gun, shaped charges may be arranged in a number of different phasing patterns. Possible phasing patterns include spiral patterns, such as 45xc2x0, 60xc2x0, or 90xc2x0 spiral patterns; two-phase patterns (e.g., xc2x190xc2x0, xc2x145xc2x0, etc.); tri-phase patterns (e.g., +45xc2x0/0xc2x0/xe2x88x9245xc2x0, etc.), and other phasing patterns. In addition, the shot density of a perforating gun system may be varied by adjusting the number of shaped charges within any given distance. For example, typical shot densities may include 4 shots per foot (SPF), 5 SPF, 6 SPF, 10 SPF, 12 SPF, and so forth. Shots per foot refer to the number of shaped charges that can be mounted in a perforating gun in a given foot.
Various types of perforating guns exist. A first type is a strip gun that includes a strip carrier on which capsule shaped charges may be mounted. The capsule shaped charges are contained in sealed capsules to protect the shaped charges from the well environment. Another type of gun is a sealed hollow carrier gun, which includes a hollow carrier in which non-capsule shaped charges may be mounted. The shaped charges may be mounted on a loading tube or strip inside the hollow carrier.
Thinned areas (referred to as scallops) may be formed in the wall of the hollow carrier housing to allow easier penetration by perforating jets from fired shaped charges. Typically, a pattern of scallops is formed in the carrier housing according to a desired phasing pattern. If a loading tube is used, holes are also formed in the loading tube according to the phasing pattern to align shaped charges to the scallops in the carrier gun housing.
Conventionally, to provide multiple shot density and phasing configurations, several variations of each type of perforating gun are kept readily available. This creates the problem of ordering and storing a relatively large number of parts, since desired types and variations of guns in adequate quantities may need to be kept in anticipation of the needs of a well operator. If a particular type of gun is not available, then well operations may be delayed while waiting for the part. Also, the unavailability of a perforating gun having a desired perforating phasing pattern and/or shot density may prevent creation of optimum perforations in a formation. Thus, a need continues to exist for improved perforating gun systems.
In general, according to one embodiment, a perforating gun system comprises shaped charges and a carrier housing in which the shaped charges are contained. The carrier housing has an outer surface defining an arrangement of scallops. A first set of the scallops provides a first phasing configuration and a second, distinct set of scallops provides a second phasing configuration.
Other features and embodiments will become apparent from the following description, the drawings, and the claims.